As commonly known, variable displacement compressors having a swash plate are used hi air conditioning systems of motor vehicles. Such compressors typically include at least one piston disposed in a cylinder of a cylinder block and a rotor assembly operatively coupled to a drive shaft. The swash plate is coupled to and adapted to be rotated by the rotor assembly. The swash plate is variably angled relative to the rotor assembly between a minimum angle and a maximum angle. Each piston slidably engages with the swash plate through a shoe as the swash plate rotates causing the piston to reciprocate within the cylinder. As the angle of the swash plate relative to the rotor assembly varies, the stroke of each piston is varied and, therefore, the total displacement or capacity of the compressor is varied. The compressor can include a hinge mechanism to couple the swash plate to the rotor.
In variable displacement compressors having a swash plate, the swash plate is typically made from a ferrous material. The ferrous material exhibits poor bearing properties when the swash plate is slidably engaging with the shoe of the piston. Therefore, copper-based coatings, polymers such as PTFE and MoS2 and thermal sprays are applied to the swash plate to provide a desired bearing interface between the swash plate and the shoe. However, use of the coatings or sprays on the swash plate increases manufacturing cost and complexity. The coating also can warp, blister, and peel causing binding or seizure between the swash plate and the shoe. Additionally, the ferrous material does not provide the swash plate with a suitable mass to facilitate an optimal moment of inertia, which consequently affects the variation of the angle of the swash plate. To overcome these limitations, a swash plate can be made from a copper alloy material such as disclosed in U.S. Pat. No. 5,974,946 to Kanou et al. However, the swash plates made from a copper alloy material are typically separate from the hub and coupled thereto by fastening means. The fastening means to couple the swash plate to the hub can warp or damage the swash plate, thus delimiting an efficiency of the compressor.
Additionally, hinge mechanisms can include support arms. For example, in U.S. Pat. No. 5,540,559 to Kimura et al., a hinge unit of a variable capacity swash-plate type compressor is disclosed. A pair of brackets protrudes from a back surface of a rotary swash plate and a pair of support arms protrudes from the rotor. One end of a guide pin is fixed to each bracket of the rotary swash plate and the other end of the guide pin is fixed to a spherical element. A circular guide hole is linearly formed in each support arm of the rotor. An inner surface of the circular hole works as a guide surface and the spherical element of the guide pin is rotatably and slidably inserted into the circular hole. However, these hinge mechanisms do not maintain a constant top clearance of the piston at a top dead center position (hereinafter “TDC”) during swash plate angle variations. Additionally, the support arms of the hinge mechanisms do not provide optimal strength to support resulting loads caused by the reciprocating pistons acting on the swash plate to militate against friction and tipping. Because a sufficient support is not provided under the resultant load, frictional forces in the hinge mechanism and tipping moments of the swash plate are created, thus also delimiting the efficiency of the compressor.
Therefore, there is a continuing need for a hinge assembly comprising a minimal number of parts that exhibits low hysteresis and provides improved balance and bearing properties of the swash plate to operatively maintain a constant TDC position of the pistons.